Auto-Dishwashing Cleaning Technique

ABSTRACT

A method of cleaning tableware in an automatic dishwashing machine comprising: 1) allowing a mist of a cleaning product, wherein the cleaning product has been atomized to a size wherein greater than 95% of the particles have a diameter less than 2 microns, to contact the food soiled tableware to be cleaned; and 2) removing the food soil on the tableware by using a cleaning fluid; and wherein the second step is to be performed after the first step. A dishwasher comprising a device capable of atomising a cleaning product, wherein the device is capable of atomizing the cleaning product such that greater than 95% of the particles are less than 2 microns in diameter.

BACKGROUND OF THE INVENTION

Alternative methods for cleaning tableware in automatic dishwashing machines have been under investigation for some time. There is a constant drive to improve such devices in terms of their cleaning performance, energy efficiency and environmental impact.

US 2005/0224098A1 discloses one such technique to improve cleaning performance. This document discloses a tableware cleaning method that utilises a fine mist of a cleaning fluid to enhance cleaning. The content of this entire document is hereby incorporated by reference. It was found that atomising a cleaning fluid into a mist and allowing the mist to contact the soiled tableware provided enhanced cleaning performance over traditional aqueous detergent solution techniques.

It was believe that the mist of cleaning fluid more readily permeates into food soils and allows for their ready removal in a subsequent cleaning/rinsing step.

It is the objective of the present invention to improve upon the cleaning technique described in this document.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved method of cleaning tableware in an automatic dishwashing machine comprising:

1) allowing a mist of a cleaning product, wherein the cleaning product has been atomized to a size wherein great than 95% of the particles have a size less than 2 microns, to contact the food soiled tableware to be cleaned in an automatic dishwashing machine; and

2) removing the food soil on the tableware by using a cleaning fluid wherein the second step is to be performed after the first step.

In accordance with another aspect of the present invention, there is provided a dishwasher comprising a device capable of atomising a cleaning product, wherein the device is capable of atomizing the cleaning product such that greater than 95% of the particles are less than 2 microns in diameter.

DETAILED DESCRIPTION OF THE INVENTION

It has been surprisingly found that by reducing the particle size of the mist of cleaning product increases the performance of the cleaning step. This performance benefit allows for the improvement of both the energy efficiency of the wash cycle and its environmental footprint.

This is because the improved cleaning performance of the finer mist may reduce the both the temperature and the quantity of the cleaning fluid used in a subsequent rinsing step.

In addition, the finer atomisation also allows for the use of less chemical cleaning product as this is dispersed much more efficiently.

It has been found that keeping the particle size of the atomized cleaning product to below 2 microns offers the substantial benefits over the cited art. The mist comprising these smaller particles much more rapidly fills the dishwasher and the mist does not require “line of sight” from a nozzle to the surface to be coated.

This allows all surfaces of the soiled tableware to encounter the cleaning product rapidly from potentially a single mist source nozzle within the dishwasher.

The potential use of only a single nozzle clearly offers cost savings in terms of the construction of the dishwasher or device placed inside the dishwasher to generate the mist.

Without wishing to be bound by theory, it is believed that these benefits derive from the fact that a smaller particle size mist behaves in a much more gas-like way than the mist that is described in US 2005/0224098A1.

The mist producing technology described in US2005/0224098A1 is not capable of producing as fine a chemical product missed as is required for the present invention.

WO2008149073 discloses a device suitable for generating atomised mists with the desired particles size of the present invention. The disclosure of these documents is herein incorporated by reference. A smaller version of these can be installed into a dishwasher. Or a smaller version may be designed as a standalone device designed to be incorporated into different machines.

Alternatively U.S. Pat. No. 8,100,191 also discloses a suitable misting device for the present invention. The disclosure of this document is also incorporated by reference.

Preferably the misting device is designed to be inbuilt into a dedicated dishwashing machine. Alternatively the device can be designed as a standalone unit for incorporation into a wide range of different dishwashing machines.

In addition to the speed of action and cost of implementation benefits of the small particle mist, it has also been found that the smaller particle size aids penetration of the atomized cleaning product into the food soils and greatly facilitates its release. Without wishing to be bound by theory it is believe that this may be the result of the smaller particles being readily able to enter much smaller pores in the food waste.

The use of the mist of cleaning product with the smaller particle size also provides for a shortened hold sequence in the cleaning while the mist works on the food stains. This allows for a much more rapid overall cleaning cycle.

Any usual detergent product may be used in the described method as the cleaning product. Non-limiting examples of suitable detergent products include an alkaline agent, a surfactant, an enzyme, and a bleaching agent.

The surfactant may be anionic, cationic, zwitterionic, or non-ionic.

The enzyme may be a protease or an amylase.

The bleaching agent may be organic or non-organic.

The cleaning product may a single entity. Or the cleaning product may be a complex mixture, of different ingredients.

These may be standard examples of reagents known in the ADW detergent art or they may be more unusual chemical components.

For example, in normal ADW detergent chemistry, anionic surfactants have to be avoided due to the dangers of foaming. In the present invention they may be used as foaming is not an issue in a mist.

The use of the mist allows for potentially more expensive components as much smaller amounts of material may be needed than in conventional water solution washing. This is because they are not being dissolved in large amounts of wash water.

For example, ionic liquids maybe used in the present invention. These are known to have good cleaning properties but are very expensive. They also have the problem that if diluted in water they revert back to salts and so they cannot normally be used in a standard dish washer. With the misting system of the present invention, the distribution of neat undiluted ionic liquid over the tableware can be achieved. A non-limiting example of suitable ionic liquids may be found in U.S. Pat. No. 7,928,053.

The detergent product may be used alone or dissolved in a suitable carrier prior to atomisation.

A suitable carrier may be a solvent. Non-limiting examples of suitable solvents include water, and ethanol.

The cleaning fluid used in the second step may be water or it may be another solvent. It is preferred that the fluid comprises water.

The cleaning fluid may be solely a solvent such was water, or the cleaning fluid may comprise further detergent or rinsing chemistry.

The cleaning fluid may further comprise detergent compositions that comprise one or more of the following ingredients:

Bleaches

Any conventional bleaching compound can be used in any conventional amount, in the composition of the invention

There may be more than one bleaching compound in the detergent compositions of the present invention. A combination of bleaching compounds can be used.

The bleaching compound is preferably present in the relevant composition in an amount of at least 1% by weight, more preferably at least 2% by weight, more preferably at least 4% weight. Preferably it is present in the relevant composition in an amount of up to 30% weight, more preferably up to 25% weight, and most preferably up to 20% by weight.

If more than one bleaching compound is used, the total fraction of bleaching compound is preferably present in the relevant composition in an amount of at least 1% by weight, more preferably at least 2% by weight, more preferably at least 4% weight. Preferably it is present in the relevant composition in an amount of up to 30% weight, more preferably up to 25% weight, and most preferably up to 20% by weight.

In the detergent compositions of the present invention the bleach compound normally depends on hydrogen peroxide or per-carbonate as a hydrogen peroxide source.

Most preferably the bleach is selected from inorganic peroxy-compounds and organic peracids and the salts derived therefrom.

Examples of inorganic perhydrates include persulfates such as peroxymonopersulfate (KMPS), perborates or percarbonates. The inorganic perhydrates are normally alkali metal salts, such as lithium, sodium or potassium salts, in particular sodium salts. The inorganic perhydrates may be present in the detergent as crystalline solids without further protection. For certain perhydrates, it is however advantageous to use them as granular compositions provided with a coating which gives the granular products a longer shelf life.

The preferred percarbonate is sodium percarbonate of the formula 2Na₂CO₃.3H₂O₂. A percarbonate, when present, is preferably used in a coated form to increase its stability.

Organic peracids include all organic peracids traditionally used as bleaches, including, for example, perbenzoic acid and peroxycarboxylic acids such as mono- or diperoxyphthalic acid, 2-octyldiperoxysuccinic acid, diperoxydodecanedicarboxylic acid, diperoxy-azelaic acid and imidoperoxycarboxylic acid and, optionally, the salts thereof. Especially preferred is phthalimidoperhexanoic acid (PAP).

The pH of the detergent composition may be between 6 and 14, preferably between 8 and 12 and more preferably between 10 and 11.

Builders

The composition may further comprise one or more builder compounds. These may be selected, for example, from the group comprising STPP, sodium citrate, sodium iminodisuccinate, sodium hydroxyiminodisuccinate, MGDA, and glutamic diacetic acid sodium salt or combinations thereof. However the invention is not limited to these builders

Preferably, the total builder quantity in the detergent composition comprises from 5% to 95% by weight, preferably from 15% to 75% by weight, preferably from 25% to 65% by weight, most preferably from 30% to 60% by weight of the detergent composition.

Oxidation Catalysts

The compositions of the invention may also include oxidation catalysts.

Some non limiting examples of other oxidation catalysts that may be used in the compositions of the present invention include manganese oxalate, manganese-acetate, manganese-collagen, cobalt-amine catalysts and the Mn-TACN catalyst. The oxidation catalysts may comprise other metal compounds, such as iron or cobalt complexes.

The skilled person will be aware of other oxidation catalysts that may be successfully combined with the detergent compositions of the present invention.

The oxidation catalysts may comprised between 0.005 and 1% by weight of the detergent formulation, preferably between 0.05 and 0.5% by weight, most preferably between 0.1 and 0.3% by weight.

Surfactants

The detergent compositions of the present invention may comprise further surfactants. These are usually non-ionic surfactants.

Non-ionic surfactants are preferred for automatic dishwashing (ADW) detergents since they are defined as low foaming surfactants. The standard non-ionic surfactant structure is based on a fatty alcohol with a carbon C₈ to C₂₀ chain, wherein the fatty alcohol has been ethoxylated or propoxylated. The degree of ethoxylation is described by the number of ethylene oxide units (EO), and the degree of propoxylation is described by the number of propylene oxide units (PO).

The length of the fatty alcohol and the degree of ethoxylation and/or propxylation determines if the surfactant structure has a melting point below room temperature or in other words if is a liquid or a solid at room temperature.

Surfactants may also comprise butylene oxide units (BO) as a result of butoxylation of the fatty alcohol. Preferably, this will be a mix with PO and EO units. The surfactant chain can be terminated with a butyl (Bu) moiety.

Preferred solid non-ionic surfactants are ethoxylated non-ionic surfactants prepared by the reaction of a mono-hydroxy alkanol or alkylphenol with 6 to 20 carbon atoms. Preferably the surfactants have at least 12 moles, particularly preferred at least 16 moles, and still more preferred at least 20 moles, such as at least 25 moles of ethylene oxide per mole of alcohol or alkylphenol.

Particularly preferred solid non-ionic surfactants are the non-ionics from a linear chain fatty alcohol with 16-20 carbon atoms and at least 12 moles, particularly preferred at least 16 and still more preferred at least 20 moles, of ethylene oxide per mole of alcohol.

The non-ionic surfactants additionally may comprise propylene oxide units in the molecule. Preferably these PO units constitute up to 25% by weight, preferably up to 20% by weight and still more preferably up to 15% by weight of the overall molecular weight of the non-ionic surfactant.

Surfactants which are ethoxylated mono-hydroxy alkanols or alkylphenols which additionally comprise poly-oxyethylene-polyoxypropylene block copolymer units may be used. The alcohol or alkylphenol portion of such surfactants constitutes more than 30%, preferably more than 50%, more preferably more than 70% by weight of the overall molecular weight of the non-ionic surfactant.

Another class of suitable non-ionic surfactants includes reverse block copolymers of polyoxyethylene and poly-oxypropylene and block copolymers of polyoxyethylene and polyoxypropylene initiated with trimethylolpropane.

Another preferred class of non-ionic surfactant can be described by the formula:

R₁O[CH₂CH(CH₃)O]_(x)[CH₂CH₂O]_(y)[CH₂CH(OH)R₂]

where R₁ represents a linear or branched chain aliphatic hydrocarbon group with 4-18 carbon atoms or mixtures thereof, R₂ represents a linear or branched chain aliphatic hydrocarbon rest with 2-26 carbon atoms or mixtures thereof, x is a value between 0.5 and 1.5 and y is a value of at least 15.

Another group of preferred non-ionic surfactants are the end-capped polyoxyalkylated non-ionics of formula:

R₁O[CH₂CH(R₃)O]_(x)[CH₂]_(k)CH(OH)[CH₂]_(j)OR₂

where R₁ and R₂ represent linear or branched chain, saturated or unsaturated, aliphatic or aromatic hydrocarbon groups with 1-30 carbon atoms, R₃ represents a hydrogen atom or a methyl, ethyl, n-propyl, iso-propyl, n-butyl, 2-butyl or 2-methyl-2-butyl group, x is a value between 1 and 30 and, k and j are values between 1 and 12, preferably between 1 and 5. When the value of x is >2 each R₃ in the formula above can be different. R₁ and R₂ are preferably linear or branched chain, saturated or unsaturated, aliphatic or aromatic hydrocarbon groups with 6-22 carbon atoms, where group with 8 to 18 carbon atoms are particularly preferred. For the group R₃═H, methyl or ethyl are particularly preferred. Particularly preferred values for x are comprised between 1 and 20, preferably between 6 and 15.

As described above, in case x>2, each R₃ in the formula can be different. For instance, when x=3, the group R₃ could be chosen to build ethylene oxide (R₃═H) or propylene oxide (R₃═methyl) units which can be used in every single order for instance (PO)(EO)(EO), (EO)(PO)(EO), (EO)(EO)(PO), (EO)(EO)(EO), (PO)(EO)(PO), (PO)(PO)(EO) and (PO)(PO)(PO). The value 3 for x is only an example and bigger values can be chosen whereby a higher number of variations of (EO) or (PO) units would arise.

Particularly preferred end-capped polyoxyalkylated alcohols of the above formula are those where k=1 and j=1 originating molecules of simplified formula:

R₁O[CH₂CH(R₃)O]_(x)CH₂CH(OH)CH₂OR₂

The use of mixtures of different nonionic surfactants is suitable in the context of the present invention for instance mixtures of alkoxylated alcohols and hydroxy group containing alkoxylated alcohols.

Other suitable surfactants are disclosed in WO 95/01416, to the contents of which express reference is hereby made.

In a particularly preferred embodiment of the present invention, the composition according to the first aspect of the present invention is one wherein the liquid non-ionic surfactant has the general formula

R₁-[EO]_(n)-[PO]_(m)-[BO]_(p)-Bu_(q)

wherein:

R₁ is an alkyl group of between C₈ and C₂₀ ;

EO is ethylene oxide;

PO is propylene oxide;

BO is butylene oxide;

Bu is butylene

n and m are integers from 1 to 15;

p is an integer from 0 to 15; and

q is 0 or 1.

Examples of especially preferred nonionic surfactants are the Lutensol™ and Pluronic™ range from BASF, Dehypon™ series from Cognis/BASF and Genapol™ series from Clariant.

The total amount of surfactants typically included in the detergent compositions is in amounts of up to 15% by weight, preferably of from 0.5% to 10% by weight and most preferably from 1% to 5% by weight.

Preferably non-ionic surfactants are present in the compositions of the invention in an amount of from 0.1% to 10% by weight, more preferably 0.25% to 7% by weight and most preferably 0.5% to 5% by weight.

Bleach Activators

Generally the use of a bleach activator in a detergent composition can lead to a significant reduction in the effective washing temperature. Compositions of the present invention may also comprise a bleach activator.

If desired therefore, the detergent compositions may comprise one or more additional bleach activators depending upon the nature of the bleaching compound.

Any suitable bleach activator or combination of bleach activators may be included. A non-limiting example of a common bleach activator is tetraacetylethylenediamine (TAED).

Conventional amounts of the bleach activators may be used e.g. in amounts of from 0.5% to 30% by weight, more preferred of from 1% to 25% by weight and most preferred of from 2% to 20% by weight of the detergent composition.

Enzymes

The composition may comprise one or more enzymes. Desirably the enzyme is present in the compositions in an amount of from 0.01% to 5% by weight especially 0.01% to 4% by weight, for each type of enzyme when added as a commercial preparation. As they are not 100% active preparations this represents an equivalent amount of 0.005% to 1% by weight of pure enzyme, preferably 0.01% to 0.75% by weight, especially 0.01% to 0.5% by weight of each enzyme used in the compositions. The total amount of enzyme in the detergent composition is preferably in the range of from 0.01% to 6% weight percent, especially 0.01% to 3% by weight, which represents an equivalent amount of 0.01% to 2% by weight of pure enzyme, preferably 0.02% to 1.5% by weight, especially 0.02% to 1% by weight of the total active enzyme used in the compositions.

Any type of enzyme conventionally used in detergent compositions may be used according to the present invention. It is preferred that the enzyme is selected from proteases, lipases, amylases, cellulases, pectinases, laccases, catalases and all oxidases, with proteases, pectinases and amylases, (especially proteases) being most preferred. It is most preferred that protease and/or pectinases and/or amylase enzymes may be included in the compositions according to the invention; such enzymes are especially effective for example in dishwashing detergent compositions. Any suitable species of these enzymes may be used as desired.

Anti Corrosion Agents

Preferred silver/copper anti-corrosion agents are benzotriazole (BTA) or bis-benzotriazole and substituted derivatives thereof. Other suitable agents are organic and/or inorganic redox-active substances and paraffin oil. Benzotriazole derivatives are those compounds in which the available substitution sites on the aromatic ring are partially or completely substituted. Suitable substituents are linear or branch-chain C₁₋₂₀ alkyl groups and hydroxyl, thio, phenyl or halogen such as fluorine, chlorine, bromine and iodine. A preferred substituted benzotriazole is tolyltriazole.

It is known to include a source of multivalent ions in detergent compositions, and in particular in automatic dishwashing compositions, for anti-corrosion benefits. For example, multivalent ions and especially zinc, bismuth and/or manganese ions have been included for their ability to inhibit such corrosion. Organic and inorganic redox-active substances which are known as suitable for use as silver/copper corrosion inhibitors are mentioned in WO 94/26860 and WO 94/26859. Suitable inorganic redox-active substances are, for example, metal salts and/or metal complexes chosen from the group consisting of zinc, manganese, titanium, zirconium, hafnium, vanadium, cobalt and cerium salts and/or complexes, the metals being in one of the oxidation states II, III, IV, V or VI. Particularly suitable metal salts and/or metal complexes are chosen from the group consisting of MnSO₄, Mn(II) citrate, Mn(II) stearate, Mn(II) acetylacetonate, Mn(II) [1-hydroxyethane-1,1-diphosphonate], V₂O₅, V₂O₄, VO₂, TiOSO₄, K₂TiF₆, K₂ZrF₆, CoSO₄, Co(NO₃)₂ and Ce(NO₃)₃. Any suitable source of multivalent ions may be used, with the source preferably being chosen from sulphates, carbonates, acetates, gluconates and metal-protein compounds. Zinc salts are specially preferred glass corrosion inhibitors.

Any conventional amount of the anti-corrosion agents may be included in the compositions of the invention. However, it is preferred that they are present in an total amount of from 0.01% to 5% by weight, preferably 0.05% to 3% by weight, more preferably 0.1% to 2.5% by weight, such as 0.1% to 1% by weight based on the total weight of the composition. If more than one anti-corrosion agent is used, the individual amounts may be within the preceding amounts given but the preferred total amounts still apply.

It is preferably that the cleaning fluid is at least 90% water and most preferably at least 99% water.

The cleaning fluid may preferably contain only rinse aid chemistry to aid the drying step.

The use of the fine mist of the present invention allows for much lower than usual amounts of cleaning fluid in the rinse step as the coherence of the food to the tableware is much reduced.

The cleaning fluid may be applied at room temperature. However the cleaning fluid may also be heated prior to use for more awkward food stains.

In a further aspect of the invention there is provided a dishwasher equipped with the misting technology of the present invention.

The technology is preferred to be inbuilt into a dishwasher to allow the necessary safety features to be included. Particle sizes in the order of 2 microns are known to interact in a detrimental manner to lung tissue. This means that while the mist is present in the dishwasher, the door should remain locked. And the entire dishwasher should be gas tight to avoid any possibility that the mist escapes to the outside.

By using the cleaning method of the present invention, the cleaning performance of removing food debris, e.g., oil debris, hardly removable, can be improved considerably. 

1. A method of cleaning tableware in an automatic dishwashing machine comprising the sequential steps of: misting a cleaning product that has been atomized to a size wherein greater than 95% of the particles have a diameter less than 2 microns, to contact food soiled tableware to be cleaned; and removing food soil on the tableware with a cleaning fluid.
 2. The method of claim 1, wherein the cleaning product comprises at least one of an alkaline agent, a surfactant, an enzyme, and a bleaching agent.
 3. The method of claim 1, wherein the cleaning fluid is at least 90% water.
 4. The method of claim 1, wherein the cleaning fluid is at least 99% water.
 5. The method of claim 1, wherein the cleaning product is obtained by dissolving at least one of an alkaline agent, a surfactant, an enzyme and a bleaching agent in water.
 6. The method of claim 1 further comprising heating the food soiled tableware.
 7. A dishwasher comprising a system performing the method of claim 1
 8. The dishwasher of claim 7, wherein the cleaning product comprises at least one of an alkaline agent, a surfactant, an enzyme and a bleaching agent.
 9. The dishwasher of claim 7, wherein the cleaning product is obtained by dissolving at least one of an alkaline agent, a surfactant, an enzyme and a bleaching agent in water.
 10. The dishwasher of claim 7 further comprising a heating unit for heating wash water, wherein the atomized cleaning product permeates food soil on the tableware after being heated by the heating unit.
 11. The method of claim 6, wherein the atomized cleaning product permeates food soil on the tableware after heating the food soiled tableware. 